There are various systems of signal reporting used by radiotelegraphers, including the following:
Introduced in the 1930s, the RST system remains the most commonly used system of signal reporting among radio amateurs. The T (Tone) number is, however, largely irrelevant nowadays as most modern transmitters have excellent tone.
2–Barely readable, occasional words distinguishable.
3–Readable with considerable difficulty.
4–Readable with practically no difficulty.
1–Faint signals, barely perceptible.
2–Very weak signals.
5–Fairly good signals.
7–Moderately strong signals.
9–Extremely strong signals.
1–Sixty cycle a.c or less, very rough and broad.
2–Very rough a.c., very harsh and broad.
3–Rough a.c. tone, rectified but not filtered.
4–Rough note, some trace of filtering.
5–Filtered rectified a.c. but strongly ripple-modulated.
6–Filtered tone, definite trace of ripple modulation.
7–Near pure tone, trace of ripple modulation.
8–Near perfect tone, slight trace of modulation.
9–Perfect tone, no trace of ripple or modulation of any kind.
If the signal is as steady as crystal control, add the letter X to the RST report.
If there is a chirp, the letter C may be added.
If there are key clicks, add K.
QRK is Readability and QSA is Signal Strength, and both are on a scale of 1 to 5. So a perfect signal is “QRK5 QSA5”. Here are the definitions:
QRK#: Your intelligibility (or that of …) is
QSA#: The strength of your signals (or those of …) is
1 (scarcely perceptible)
3 (fairly good)
5 (very good)
A shorter form of QRK is just Q#, ranging from Q1 (if unreadable) up to Q5 (perfect copy).
RSN is an attempt by some Australian radio amateurs to try and address the shortcomings of RST. The “N” stands for Noise. Because virtually all transmitters now have perfect Tone, the T is seldom useful – but we do have very high levels of Noise these days.
As an example, if we send a report of RST 369, the other guy has no way of knowing why his readability is mediocre. Is it QRM? QRN? QSB? Perhaps even QSD?
By sending a report such as “RSN 368,” he will understand that, although his strength is a respectable S6, the Noise is stronger at S8, so he’s losing the battle.